1. Field of the Invention
The present invention relates generally to a gate turn-off thyristor of an amplifying gate structure type and more particularly to a gate turn-off thyristor provided with a quick turn-on time and a quick turn-off time, that is, a large di/dt (current rise rate) capability at both the transient periods of turn-on and turn-off.
2. Description of the Prior Art
Generally, a gate turn-off thyristor is made up of four PNPN layers (three P-N junctions) and provided with an anode electrode A, a cathode electrode K, a first gate electrode G.sub.1 disposed at the auxiliary thyristor portion and a second gate electrode G.sub.2 disposed at the main thyristor portion. When a forward voltage is applied between the anode electrode A and the cathode electrode K and a triggering gate signal voltage is applied between the first gate electrode G.sub.1 and the cathode electrode K, the resulting gate current flowing between the gate electrode G.sub.1 and the cathode electrode K causes the thyristor to turn conductive. This turn-on operation of the thyristor takes place as follows: the resulting gate current first turns on a small area of the thyristor nearest to the first gate electrode G.sub.1 and the cathode electrode K and then the thus generated conductive area expands throughout the whole body of the thyristor. In such a gate turn-off thyristor as described above, the controllable current value I.sub.ATO is the most important factor, which is represented by the magnitude of load current which can be turned off.
In order to improve the controllable current value I.sub.ATO, a gate turn-off thyristor of buried low-resistance layer type is well known. However, in this type of thyristor, the more the controllable current value I.sub.ATO or the shorter the turn-off time, the longer the turn-on time. The desirable gate turn-off thyristor characteristics are such that a large load current must be turned on or off by a small gate current during a short rise time or a large di/dt capability. In other words, the turn-on characteristics of the thyristor is contradictory to the turn-off characteristics thereof. Therefore, it is essential to improve both the turn-on and turn-off characteristics at the same time.
A more detailed-description of an example of prior-art PNPN-semiconductor layer gate turn-off thyristor of buried low-resistance layer type will be made with reference to the attached drawings under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.